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Security Fundamentals & Crypto · Intermediate

Internet Protocol Security (IPsec)

Suite of protocols that authenticates and encrypts IP packets, used mainly for site-to-site and remote-access VPNs.

Definition

IPsec uses IKE to negotiate security associations, AH for integrity and authentication, and ESP for confidentiality plus integrity. It operates in transport mode (protecting the payload) or tunnel mode (encapsulating the entire packet). It works at Layer 3 and is transparent to applications.

Example

Two branch routers build an IKEv2 IPsec tunnel using AES-256-GCM and DH group 20.

Exam tip

Tunnel mode for site-to-site gateways; transport mode for host-to-host. ESP encrypts, AH does not.

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